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Jeffrey Davison 21st June 2012 06:01 AM

Single Tube Amp
I have some leftover parts from a still born project of a couple years ago and was thinking of scavaging it for a new project.
I have an unused pair of EML 20B DHT tubes that I thought might be a good basis for a single tube amplifer.
Searching the web I found a couple of examples, but not a lot of detail.
Anyone here ever throw one together?


dsavitsk 21st June 2012 07:33 AM

mu is really not high enough for use without a driver of some sort.

tinitus 21st June 2012 07:40 AM

not a lot of info, but just about enough to figure it out

Oleg's EML 20B SET Stereo Amp

that is, if its worth the trouble
those tubes wont last forever
or very short if less lucky
needed OPTs are far from optimal(high impedance)
still lots of expencive parts

my approach would be use as driver in a design where they could be easily replaced by a different driver tube, without major changes in the output stage

or simply build a seperate preamp/driver stage with them

kevinkr 21st June 2012 04:38 PM

As I recall the rp is fairly high making sourcing a good wideband OPT problematic.

pieter t 21st June 2012 06:40 PM


Originally Posted by kevinkr (
As I recall the rp is fairly high making sourcing a good wideband OPT problematic.

Comparable to a 211 as far as Rp is concerned, but even higher mu so the Miller capacitance will play a role.
When relieved from bass duties things would get better.
Other possibility would be a parafeed circuit, or if you hate capacitors: a 1:1 transformer followed by a "smallish" output (step-down) transformer :crazy:

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